The invention relates to a method of improving radio connection quality in a cellular radio network comprising a base station system, a subscriber terminal and a bidirectional radio connection using a directional antenna beam between the base station system and the subscriber terminal, in which method a direction of arrival of the antenna beam directed on the basis of a radio signal received uplink, transmitted by the subscriber terminal is formed in the base station system, and the base station system transmits a radio signal downlink to the subscriber terminal in the direction of transmission formed on the basis of the direction of arrival, and in forming the direction of transmission a preknown number of previously formed directions of arrival are utilized.
The above-described arrangement has a drawback that it functions best when the radio connection between the base station system and the subscriber terminal is balanced, i.e. radio signals pass regularly and symmetrically in both directions. A problem with radio connections comprising occasional and/or asymmetrical traffic is that the direction of transmission does not necessarily correspond to the actual location of the subscriber terminal, since a long time may have passed from the latest signal received from the subscriber terminal. Meanwhile, the subscriber terminal may have moved to the extent that the signal transmitted using the direction of transmission formed on the basis of the old direction of arrival will no longer reach the subscriber terminal.
The drawback is serious particularly in cellular radio networks employing packet transmission: typically when packet transmission is performed, one party, for instance the base station system, transmits large amounts of data, and the subscriber terminal eventually transmits only occasional retransmission requests. For instance, use of a WWW (World Wide Web) browser produces heavy downlink traffic and only light uplink traffic.
The object of the invention is to provide a method and equipment implementing the method in such a way that the above drawbacks can be solved. This is achieved with a method of the type set forth in the preamble, which method is characterized in that when forming a direction of transmission, each previously formed direction of arrival is weighted in inverse proportion to the temporal distance of the direction of arrival from a known reference time instant.
The invention further relates to a cellular radio network comprising a base station system, a subscriber terminal and a bidirectional radio connection using a directional antenna beam between the base station system and the subscriber terminal, and the base station system forms a direction of arrival of the antenna beam directed on the basis of a radio signal received uplink, transmitted by the subscriber terminal, and the base station system transmits a radio signal downlink to the subscriber terminal in the direction of transmission formed on the basis of the direction of arrival, and the base station utilizes a preknown number of previously formed directions of arrival in forming the direction of transmission.
In accordance with the invention, the cellular radio network is characterized in that in forming the direction of transmission the base station system is arranged to weight each previously formed direction of arrival in inverse proportion to the temporal distance of the direction of arrival from a known reference time instant.
The preferred embodiments of the invention are disclosed in the dependent claims.
The invention is based on the idea that when calculating the direction of transmission on the basis of the directions of arrival, not only a given number of directions of arrival are considered, but every single direction of arrival is considered weighted with its significance. Significance is determined as a temporal distance of the direction of arrival from a known reference time instant, e.g. from the last formed direction of arrival.
Several advantages are achieved with the method and arrangement of the invention. The method improves the performance of directional antenna beams in radio connections comprising occasional and/or asymmetrical traffic, particularly in packet switched radio systems.